a) Field of the Invention
This invention relates to a flavone derivative or a salt thereof, which is useful as a medicine.
b) Description of the Related Art
Peptidoleucotrienes LTC.sub.4, LTD.sub.4 and LTE.sub.4, a group of metabolites of arachidonic acid, are known to act as important causal substances for bronchial asthma both in vitro and in vivo (Henderson, W. R., Jr. Ann. Intern. Med., 121, 684-697, 1994). As morbid conditions caused by leucotriene, there are airway constriction, mucosal oversecretion and pulmonary edema. They eventually induce an airway disorder which is a characteristic of asthma. Effects of LTC.sub.4 or LTD.sub.4 on airway constriction when inhaled reach 1,000 times as much as those of histamine. LTE.sub.4 has lower activities compared with the other leucotrienes, but airway constriction induced by LTE.sub.4 is long lasting compared with that caused by the other leucotrienes (Larsen, J. S., Acosta, E. P. Ann. Pharmacother, 27, 898-903, 1993).
Further, leucotrienes are stated to take part not only in asthma but also in various allergic diseases, autoimmune diseases, inflammatory diseases, cerebral ischemia, cerebral apoplexy and the like.
Keeping in step with discovery of roles of leucotrienes in biosynthesis pathways and diseases as mentioned above, there are increasing activities for the development of synthesis inhibitors for leucotriene, antagonists for cys-LT.sub.1 receptor and the like with a view to reducing leucotrienes (Metters, K. M. J. Lipid Mediators Cell Signalling, 12, 413-427, 1995). According to some recent findings in clinical aspects, it has been indicated that cys-LT.sub.1 receptor antagonists are extremely effective for various types of asthma (Taylor, I. K. Thorax, 50, 1005-1010, 1995; Pauwels, R. A., Joos, G. F. J. C. Allergy 30, 615-622, 1995). It is however the current situation that no compound has been found to be fully satisfactory in controlling action of leucotrienes.